CO has a pretty good revenue management system. The prices vary widely over time. They are actually high for advance purchase way in advance. These days you might get a better deal buying a week before - if the flight is light. I think what CO is doing is selling unsold seats at low prices - likely competing on Orbitz were cost sensitive folks can compare a week before. This process fills up the seats with otherwise no revenue. CO does this too on international flights - I believe through brokers.